Figure 1 : Chelidonum majus near the Chateau de Nidau, in the commune of Nidau just across the Thiel Canal from Biel/Bienne.
This report continues in the long tradition of amateur botanists recording the plant life in their region. The first survey period between June and September 2020 focused on the Suze river and its Madretschkanal variant in Biel/Bienne. The second set of surveys were conducted between February 2021 and September 2021 and included a wider geographical scope around the municipality of Biel/Bienne. The objective was to construct an initial dataset on the remnant flowering plant populations growing in different green spaces around the city of Biel/Bienne to understand the floral composition of the municipality.
There is a worldwide biodiversity crisis that has not spared the flora and faune of Switzerland. It has been known for some time that the flowering plants as a whole are not an exception; In 2010, the IUCN Redlist report on the conservation status of Swiss vascular plants concluded that:
Overall, every single RedList documents a manifest and sustained loss of species diversity at national level. Most threatened species appear to be bound for further losses – with no likelihood of this trend being reversed in the short term. In other words, the requirement enshrined in the Swiss Constitution that animal and plant species be prevented from going extinct has not been fulfilled.
Ten years later, after identifying widespread local extinctions that irreversibly harm genetic diversity of plant populations and precede general extinctions, researchers concluded {cite}Hicks_2020:
Our study presents clear evidence that current efforts to conserve threatened plant species are insufficient to achieve national and international targets (Convention on Biological Diversity (CBD), 2011; Swiss Biodiversity Strategy 2012) for maintaining biodiversity. The current paradigm of protecting and restoring threatened habitats is failing to avert extinctions. Going forward, we need to develop a comprehensive landscape approach, involving the creation of ecological infrastructure and translocation and assisted migration of threatened species into suitable habitats.
In Switzerland the vascular plants that are most threatened are aquatic or semi-aquatic {cite}Bornand_2016. Widespread modification of waterways, the spread of invasive species, agricultural run-off, development of shorelines and regulation of water levels has led to the decline of suitable habitats and subsequently some 70% of species are evaluated as threatened to some extent in the 2016 Redlist. Species associated with traditional forms of agriculture and land management, namely species in low altitude prairies, ruderal areas, and cropland/vineyards, which have largely dissapeared in the past 100 years, range from 40% - 60% threatened (Ibid). The decline of these species follows directly from changing agricultural practices. The species of least concern are associated with alpine habitat, rockfalls, and other largely undisturbed habitat that have historically been relatively spared from encroachment (Ibid). All of this is unfolding against the backdrop of accelerating climate change that researchers expect will provoke a major shift in habitat distributions and be a medium-term stress factor for a significant number of Switzerland's vascular plants {cite}Vittoz_2013.
Figure 2 : This figure taken from Infoflora's 2019 Regional Redlist shows the assessed threat level of the different plants in each of Switzerland's regions. We see that the middle plateau / central plateau (MP) has the highest number of plants rated higher than "LC", or least concern, followed by the Jura (JU)
The heart of Switzerland's population and economic output, the Middle Plateau is also where localized extinctions are most prominent. Some 60% of the vascular plant species evaluated for the IUCN's Redlist in the Central Plateau are classified as potentially or actually regionally threatened, followed by the Jura region with 50% {cite}Infoflora_2019. Again, species associated with freshwater habitats are the group of most concern, with some 3/4 of species under potential threat. Around 60% of the alpine populations that survive throughout the plateau, are evaluated as under potential threat, as are just over half of lowland grassland species, and nearly half of forest species {cite}Infoflora_2019. Increased levels of output and consumption, as well as relatively intensive agricultural practices, are identified as the main drivers of risk for regional biodiversity. Not all of this is due directly to higher anthropogenic pressures: the central plateau hosts isolated, localized populations that are inherently more vulnerable to pressures on their populations (Ibid).
A judicious use of public spaces, such as road verges, railroad berms and parks, that balances their potential as habitats with the needs and requirements of the city's inhabitants can mitigate some anthropologic pressure. Allowing spaces to go un-mowed, sowing native wild-flower beds, and creating micro-habitats throughout urban and suburban areas can benefit both herbaceous and predatory insects {cite}Sattler_2011. In fact, (sub)urban green spaces and road verges can provide plants, insects, and birds with suitable conditions to pursue their life cycles and even become a "last refuge" for certain species (ibid). Further, the most recent data of nationwide biodiversity provided by the Biodiversity Monitoring System shows a decline in urban vascular plant species diversity {cite}FOEN_2020. While private gardens clearly provide refuge for native species, research also shows that private gardens are heavily biased towards non-native plants, potentially making public spaces even more important as a suitable refuge for remnant wild species. As such, improvement and maintenance of areas in and around urban centers could yield outsized results in terms of biodiversity preservation at this critical juncture for the future of ecosystem services.
There are a number of different strategies that municipalities can use to boost wildflower diversity with different input costs and outcomes. For exmaple, three comparable strategies are (1) the sowing of annual wildflowers (2) the planting and maintenance of (native) perennials and (3) reducing mowing frequencies to allow for seed formation and deposition. A comparitive study of the three outcomes showed annual wildflower patches strongly dominated by native perennial patches and reduced mowing frequences, with remnant populations providing resources during the crucial early months of Spring than either perennial or annual wildflower patches. In fact, annual wildflower strips ploughed during the winter period can act as an ecological trap for overwintering arthropods who are killed during the process: one study found nearly 70% of beetles failed to emerge from hibernation in wildflower strips managed in this way{cite}GANSER2019123. Perennial wildflower strips on the other hand were found to provide signficant habitat for arthropods (Ibid). Research from the ETHZ conducted in wildflower remnants in Zürich noted significant effects of sown wildflowers on the gene pool of native plants and
In the first year, the focus was primarily on the urban Suze river and its Madretschkanal variant in Biel/Bienne. Along this stretch of the river there are many varied habitats, ranging from deep shade to full pavement to flower strips maintained for ecological and aesthetic purposes. The sites are managed by the municipality to a greater or less degree and all areas surveyed were open access to the public and reasonably accessible for an average person. In 2021 the surveys included a wider geographic scope, but still focused on the Madretschkanal and the urban Suze river. The zones surveyed ranged from railroad berms to green areas in and around sidewalks and renaturalization sites. As such, the sites varied greatly in size and shape.
Figure 3 : Map of survey locations around Biel/Bienne in 2020 - 2021. Note that some surveys occured outside the scope of this map and the heavy focus on the Suze river and the Madretschkanal branch, as well as the Madretch quarter of Biel/Bienne in particular.
Figure 4 : Images of three survey sites along the urban Suze river and the Madretschkanal. There was a great diversity in survey site characteristics amenable to many varieties of plants.
The size of the sites was not recorded, but a detailed description is available. In nearly all cases it is also possible to recover the boundary of the sites based on the geometry of the object as surveys were usually bounded by sidewalks, roads, or other barriers. Larger features, such as those in the photos above, were typically broken into smaller sites and surveyed individually to give some idea of the variation (or lack thereof) along a given feature. Sometimes the survey sites are small and isolated as in the features surveyed in Zukunftstrasse shown below on the right. While this data is not directly accessible in this analysis for the various survey sites, it can be reconstructed from the survey notes and the satellite imagery.
Figure 5 : Three examples of the decomposition of city features into survey sites. Left : The concrete driveway and the bend in the Madretschkanal make natural separations in the three survey sites. Middle : Shows the survey sites at the Flösserweg lot. It was surveyed three different times in four different locations. Right : Two different feature types were surveyed at this location near Zukunftstrasse: Three raised garden beds put in by the city to slow street traffic, and two isolated river bank sites.
A site was inspected for the vascular plants in flower, and all the different species identified were recorded. Throughout the survey period, only plants in flower were identified in order to increase the reliability of observations. The exceptions were some trial tree identifications, shrub identifications (such as the genus Nitida, Taraxacum), and Hedera helix, which is imminently recognizable and is common throughout survey locations. Most of these non-flower identifications are to the genus level only. Note that Poaceae and Juncacea (grasses and sedges) were left off the survey entirely due to the difficulty in identification. For all species, the subspecies were not recorded. The below algorithm was repeated for all flowering plants on a survey site:
Nearly all plants could be identified following this algorithm, which became increasingly efficient as time went on. In June 2020, the number of plants that could be reliably identified by the surveyor was small, whereas by August 2020, the surveyor could reliably identify the common species that dominate the landscape. This meant that the 2020 - 2021 observations are not directly comparable as the surveyor was able to record a significantly higher number of species during the second year. In addition, as the number of species that were recognizable without the need to consult an algorithm or a guidebook increased, the surveys became increasingly quick. Some direct results of this data collection protocol are the following:
It was decided to not use transects or gridsquares and avoid estimating the relatively proportion of different plant populations. As noted in the previous section, this is mitigaged by the strategy of taking multiple surveys across large urban features allowing some indication of the distribution to be oberved in the data. The geometry of the sites is easy to recover in the vast majority of cases using the surveyor's field notes and aerial photographs / satellite imagery.
Figure 6: Summary statistics for the first year of surveys. Left : The number of unique species, unique samples, and unique sites surveyed per month in year 1. Top right: The number of species identified per survey per month in year 1. Bottom right: Summary statistics of year 1.
Figure 7 : Same chart as the previous but for year 2. Notice the survey period began in February rather than June and the significantly increased number of observations across all metrics.
This analysis follows the classifications of Infoflora. The first major distinction is between native and non-native plants: all species that arrived after 1500 (the discovery of America) are considered non-native / non indigenous. Since native species are evaluated under the IUCN Redlist, it was assumed that any species on the Redlist is a native species. Aside from the quite small category of "ns" (5 observations, or .08% of all species identified), which includes non-native but culturally valuable species (such as tulips that grow in humid meadows) and the few native species not included in the IUCN red list, all species fall into either (1) the native species with their conservation status characterized by an IUCN Redlist attribute or (2) non-native species characterized by their potential to become invasive. Throughout the survey period most species identified were native and classified as "Least Concern" according to the latest IUCN Redlist data. This is in line with what might be expected: the survey would likely identify populations of hardy, common plants resistant to anthropogenic pressures. As can be seen in the charts below, the general proportion of the categories remains the same between the different years and across months, with some variation as will be seen in the following sections.
Figure 8 : Categorization of the species identified plotted by month. Left: The number of unique species broken down per month and per classification category for 2020 surveys, Top right: The number of unique species broken down per month and per classification survey for the 2021 surveys. Bottom: The number of unique species identified per survey plotted monthly.
The vast majority of non-native plants are also not invasive and most have little to no chance of establishing spontaneous populations in the wild or in urban spaces. One example of a common non native, non-invasive plant, classified as ni in the chart below, is the annual Conyza canadensis (Erigeron canadensis) from North America that thrives in disturbed areas around the city. It was identified in 12 locations in August and September 2021, however these numbers underplay the relative amount of the plant in a given location as it spreads quickly and can dominate a given area during the late summer. Despite this dominance, the plant generally cedes its place to normal succession processes as time passes and thus is not considered invasive. Another two common examples of non native species that have succesfully naturalized without becoming invasive are Onobrychis viciifolia, common in fields and along road verges in late spring and early summer, and Eupatorium cannabinum, common along road verges and river banks. Both of these latter plants are available as "wild type" and are available in seed mixes for renaturalization and wildflower area creation.
Figure 9 : Three different common non-native, non-invasive plants that grow in different environments around Biel/Bienne.(Left to right) O. viciifolia is commonly found in blooms in fields, road and railroad berms in late spring; C. canadensis is an annual common in lots and highly disturbed areas; E. cannabinum thrives along river banks and in more humid areas and can bloom throught the late spring and summer.
Of all non-native species a small number are considered invasive. They must be able to reproduce in the wild and pose a threat to humans and local ecosystems. Usually for invasive plants this is through displacement of plant populations - the invasive species takes over a given area and native species have difficulty pushing it out. Info Flora maintains a list of the current watch list and black list species, a number of which were identified over the course of the survey. Some of them were purposefully planted, such as the rows of Mahonia aquifolium throughout Biel/Bienne's Madretsch quarter. Others have moved in of their own accord such as Solidago canadensis and Erigeron Annuus.
Invasive species in this study is defined as those species classified as either being on the Watch List (WL) or the Black List (BL) from the 2014 list compiled by Infoflora and the FOEN. Many more instaces of BL species were recorded than WL species throughout the course of the survey period, as can be seen in the below chart and tables. Te most important take away is that invasive species are driven by a few key species, namely Erigeron annuus (BL), Solidago canadensis (BL), Senecio inaequidens (BL), Buddleja davidii (BL) and Mahonia Aquifolium (WL), with E. annuus twice as common as its nearest competitor, S. canadensis. The most common WL species was M. aquifolium and is both very distinctive and had been widely planted by the municipality in preceeding decades.
Figure 10 : Three common species of invasive plants found throughout the city. While all three of them spring up sontaneously, M. aquifolium was planted purposefully throughout the city and dominates some areas in Madretsch, such as Kreuzplatz.
One interesting absence across all survey locations was Reynoutra japonica, a member of the Blacklist (BL). An aggressive invader of riverbanks and increasingly common throughout waterways in Switzerland, only one stand was identified near the Mettmoos park in Längholz. The following tables and charts summarize the BL and watchlist (WL) species identified over the course of the surveys. Note that Watchlist dynamics is driven by M. Aquifolium and BL dynamics are driven by a few species, but especially E. Annuus, followed by Solidago canadensis and Senecio inaequidens.
erigeron-annuus 138 solidago-canadensis 57 senecio-inaequidens 40 buddleja-davidii 25 robinia-pseudoacacia 11 prunus-laurocerasus 5 reynoutria-japonica 2 prunus-serotina 2 rubus-armeniacus 1 artemisia-verlotiorum 1 impatiens-glandulifera 1 heracleum-mantegazzianum 1 solidago-gigantea 1 Name: species, dtype: int64
mahonia-aquifolium 47 sedum-spurium 3 symphoricarpos-albus 2 parthenocissus-inserta 2 Name: species, dtype: int64
Top left : Number of invasive species identified per month in year 1. Top right : Number of invasive species identified per month in year 2. Bottom : Number of unique invasive species identified per survey for both years.
Figure 11: The above tables of the Black List and Watch List species demonstrate that the overall abundance of invasive species in the survey locations was driven by a few key species.
In most cases either no invasives or only one invasive species was found in each survey. This is constant across months and across years. Since only a handful of invasives are driving these numbres, it is clear to that the higher numbers of invasive species identified in June, July, August and September corresponds to the flowering season of E. Annuus, S. canadensis and S. inaequidens
Figure 11 : The numbe of invasives identified over the course of the survey. The top left and top right give the number of times an invasive species was identified in each month, the bottom chart gives the number of invasive species per survey over the course of the two years.
The IUCN Red List is an internationally comparable ranking of the conservation status of individual species and biotopes. Infoflora worked with the IUCN to create a national redlist for Switzerland, last updated in 2016. This analysis was complemented in 2019 with the publishing of regional redlist report. This regional redlist data provided a IUCN redlist rating for each native species in each of Switzerland's main biogeographical regions. In the previous analysis of redlist species, the national rating was used as around 500 observations in the Jura and Northern Alps were included in the surveys. As Biel/Bienne is located on the middle plateau, this section uses only observations made within the middle plateau region and categorizes them according to this regional redlist analysis. This is still the vast majority of survey locations and species identified - about 7000 observations total.
Figure 12 : Some examples of native species found throughout Biel/Bienne. From left to right: D. Pilosella, Anemone nemorosa, Epilobium dodonaei
As noted in the introduction, the regional redlist for the central plateau ranks many species on a higher risk classification than the national redlist as many populations are under more threat on the central plateau than in other biogeographic regions. While species in each category were identified, the vast majority of native species were of least concern. Compared to using the national redlist ranking, the overall results do not change, with only a few species moving from Least Concern to Near Threatened.
Figure 13 : The number of native species identified over the course of the surveys and their classification by Redlist status. The top charts gives the number of native species identified per month per year, while the bottom chart gives number of native species identified per survey over the whole time period.
To put the observations in context, according to Infoflora, 1207 different vascular plant species were identified in the 100 square kilometers roughly centered on Biel/Bienne. Of these species, some 750 were not identified on the plant surveys and about 100 species were identified in the surveys but not included in Infoflora's list of observations. While a great part of this mismatch is due to the surveyor not identifying most trees and grasses, it also indicates a significant floral diversity in the region that was not identified in the surveys. It also indicates that Infoflora may be underestimating the diversity of plant species in urban spaces, even if this diversity comes from commercial seeds and non-native plants.
Some general conclusions that can be drawn from the data are the following:
Plant surveys need to be done systematically and year on year as weather and other random factors significantly affect the population distributions of vascular plant species. The first survey year, 2020, coincided with the warmest year on record in Switzerland, tied with 2018, with a scarcity of rainfall. Meanwhile, 2021 saw the wettest and coldest spring and summer weather for many local records. It is thus to be expected that these extreme variations would result in different plant species being identified across Biel/Bienne as a whole and even in certain survey locations. One anecdote of this is a regionally Near Threatened species, Dipsacus pilosus, which was identified near the Ile de la Suze on the banks of the Suze river in 2020, however in 2021 the site was submerged for much of the survey period due to the extra rainfall and there was no sign of its presence. While this sort of data can begin to be teased out by comparing the roughly 50 sites that overlap between 2020 and 21, the overall year on year analysis should wait until the 2022 data can be gathered.
The microlevel nature of these surveys allows for a neighborhood by neighborhood and block by block analysis of plant resources in the city. Similarly, features such as road verges, rail road berms, and parks can be compared across the city. Some of this analysis will be done in a separate notebook for the 2021 data using some features already keyed to the observations. In addition, there are clear and direct extensions thanks to rich sources of data available from municipal authorities that could allow explanatory causes to be determined and differentiated site treatments to be evaluated. One example that will be addressed is that ProNature grazes sheep on select railroad berms - are there differentiated levels of diversity in these locations compared to surrounding non-treated sites? The additional data that should be explored is the following:
In short, there are a number of interesting extensions to this analysis, some of which are possible with the available data and some of which will require integration with other datasets or collection of additional data. Plant surveys will begin anew in mid February 2022. Due to the surveyor's experience, it is expected to match or exceed the observations made in 2021, which will provide a strong year on year data set of species make-up in different locations.
Currently enrolled as a master student at the Oeschger Center for Climate Change Research at the Universität Bern, these surveys will serve as the foundation for my thesis work on (sub)urban plant populations in times of significant climate change. Previously trained as an economist these surveys have also been an avenue to quickly developy my knowledge of the local flora, culminating in receiving the first-level accreditation, Bellis certificate, from the Swiss Botanical Society in 2021.
Qustions ? Comments ? Feedback most welcome at thor.erismann @ gmail.com